Regulating transformer



June 20, 1961 w. A. KOLLMANN REGULATING TRANSFORMER 5 Sheets-Sheet 1 Filed July 17, 1957 E OHM J INVENTOR. Werner A.Kollmonn AG NT June 20, 1961 w. A. KOLLMANN 2,939,685

REGULATING TRANSFORMER Filed July 17, 1957 5 Sheets-Sheet 2 INVENTOR. Werner A. Kollmonn BY LI M7 AGENT.

June 20, 1961 w, KOLLMANN I 2,989,685

' REGULAT'ING TRANSFORMER Filed July 17, 1957 5 Sheets-Sheet regulafed winding noh regulated winding fed from V 'W INVENTOR. Werner A-Kollmonn June 20, 1961 w. A. KOLLMANN 2,989,685

REGULATING TRANSFORMER Filed July 1'7, 1957 5 Sheets-Sheet 4 H V non regulated winding 7 regulated winding INVENTOR.

Werner A. Kollmunn AGENT United States Patent REGULATING TRANSFORMER Werner A. Kollmann, Weiz, Styria, Austria, asslgnor to Elin Aktiengesellschaft fiir Elektrische Industrle, Vienna, Austria, a joint-stock corporation of Austria Filed July 17, '1957, Ser. No. 672,457

Claims priority, application Austria July 27, 1956 13 Claims. (Cl. 323--'43.5)

This invention relates to three-phase transformers and particularly to three-phase transformers consisting of a main transformer and regulating one-phase transformers.

The voltage control on transmission lines may be obtained by tapping one side of the feeding transformer and change its ratio by a usual tap-changing equipment to adapt the voltage to the varying requirements of the load. On the other hand it is known, especially for regulating transformers having great capacity, to allot the voltage control to an auxiliary transformer connected in series to the main transformer (therefore hereafter called a series transformer), because it isdifficult to place the regulating coils on the main transformer core and moreover to provide suflicient space in the tank for the connecting leads to the tap changer without exceeding the railway loading gauge. Such series transformers are separated from the main transformer or may be located within the main transformer tank saving in this way bushings for the connecting leads. In a three-phase system a regulable three-phase series transformer replaces the regulating windings of a directly regulated transformer and, for a small regulating range, said series transformer, in general, may be placed yet within the tank of the main transformer preferably on its smaller side. For a small regulating range, moreover, it is possible, in general, to install the tap changer in the common tank over the series transformer. With increasing capacity of the series transformer, however, a three-phase series transformer becomes to broad, so that difficulties result in view of the loading gauge if an installation within a common tank is desired. Moreover, in such a case, there would not remain sufficient space over the series transformer for lodging the tap changer, so that the tap changer has to be installed by the side of the series transformer. A larger (longer) tank and therefore an increased but to a great extent not utilized tank volume will result from such an arrangement.

It is one object of this invention to show a way for avoiding said difficulties and enabling the installation of the regulating series transformer in the tank of the main transformer also for larger regulating ranges. It is an other object of this invention to replace the conventional regulating three-phase series transformer by two singlephase series transformers connected in the manner of the Scott system or V-connection.

This invention will be better understood when the following description is read in conjunction with the accompanying drawings, in which:

FIGURE 1 is the vector diagram for grounding adjustments of a star-star transformer with tertiary winding using, series transformers in Scott connection according to this invention, FIGURE la is the vector diagram for the nonregulated main transformer winding, FIGURE lb is the vector diagram for the main transformer winding with regulated grounds, FIGURE is the vector diagram of the delta-connected tertiary winding of the main transformer;

FIGURES 2 and 3 show circuit diagrams for regulation in conformity with the vector diagrams of FIGURE 1, FIGURE 2 for a regulation using three taps, and FIGURE 3 for a regulation for boosting and bucking the scrim windings and using only two taps;

FIGURE 4 shows the circuit diagram of a zigzagconnected choke, the object of which shall be explained later;

FIGURE 5 shows the spatial arrangement of the main transformer and the series transformers in a common tank;

FIGURE 6 shows the vector diagram for a regulation according to this invention when the winding to be regulated is zigzag-connected;

FIGURE 7 shows vector diagrams for ground regulation according to this invention using a V-connection;

FIGURE 8 shows the circuit diagram for regulation in conformity with the vector diagrams of FIGURES 7a and b;

FIGURES 9, 11 and 13 show vector diagrams for the application of the inventive idea when the winding to be regulated is connected in delta;

FIGURES 10, 12 and 14 show the circuit diagrams for regulation in conformity with the vector diagrams of FIGURES 9, l1 and 13, respectively, and

FIG. 15 is a schematic circuit diagram showing the circuit of FIG. 2 when used with a five-legged transformer.

The circuit diagrams are so laid out that the directions of the coil axes in all instances coincide with the directions of the vectors of the voltages induced therein. Thus, parallel coils are arranged on the same core, and traversed by the same flux, even though this may not be indicated. Consequently, the terminals of the coils correspond to the terminals of the associated voltage vectors in the corresponding vector diagram.

In FIGURE 2, U V W are the terminals of a starconnected, non regulated primary winding of a main transformer, U V W the terminals of its regulated secondary winding consisting of basic winding sections 1', 1", 1" and of winding sections 2, 2", 2! which may be switched in. In series with the main transformer secondary windings 1" and 2" lies a tapped secondary winding of a teaser transformer H of a Scott connection, and in series with the main transformer secondary windings 1, and 1" are two secondary windings having an equal number of turns of the main transformer B of the Scott connection. The primary windings of the teaser transformer and the main transformer are fed by a tertiary winding of the main transformer having terminals U V W in such a way that the voltage vectors of the regulated main transformer windings, of the Scott-teaser transformer and of the Scott-main transformer add geometrically as is seen in FIGURE 1b. Thus the voltage of the teaser transformer H is in phase with the voltage induced in the winding having the terminal V and the voltage of the Scott main transformer B is in phase with the voltage between the terminal W and the midpoint of the winding having the terminal V The secondary windings of the teaser transformer and of the Scott main transformer are controllable by the variable taps St St St All three variable taps are conductively connected. The secondary voltage of the teaser transformer H, regulated by the position of the tap S5, is divided in the ratio 1 to 2 by a choke Dr in parallel to the active part in-circuit section of the secondary winding of the teaser transformer. The tap point M of the choke is grounded.

FIGURE 3 shows a modification of the regulation according to this invention also for ground regulation and using a Scott connection. There are again U V W U V W and U V W the terminals of the three main transformer windings, and B and H the main transformer and the teaser transformer, respectively, of the Scott connection. The primary windings of the main transformer and of the teaser transformer are fed as in 2,989, ass

the circuit according to FIGURE 2. The circuit according to FIGURE 3, however, differs from the circuit according to FIGURE 2 in that the voltage of the Scott main transformer is not divided by using two secondary windings of equal number of turns and conductively connected by adjustable taps but by a choke Dr, dividing the adjusted secondary voltage of the Scott main transformer in the ratio of l to l. The ground of the regulated system is obtained using again a voltage divider choke Dr which subdivides the adjusted secondary voltages of the teaser transformer in the ratio of 1 to 2 (tapping point M).

The chokes Dr in FIGURES 2 and 3 make available the grounded point as does the choke Dr in FIGURE 3 may be replaced by a zigzag-connected choke, as shown in FIGURE 4. The terminals X, Y, Z, M of such a zigzag choke would have to be connected to the corresponding terminals of the circuits of FIGURES 2 and 3. The neutral point M of said choke brought out to a terminal is then the ground of the regulated system. In the case of the modification according to FIGURE 4, the secondary winding of the teaser transformer 4 has to be dimensioned for only /3 of the teaser transformer voltage required without using such a zigzag coil.

The invention is also applicable to a regulation of a zigzag-connected main transformer winding. FIGURE 6 shows the vector diagram for such a regulation, FIGURE 6' and the circuit diagram belonging thereto is identical with one of the circuit diagrams of FIGURE 2 or 3, with exception of the zigzag connection of the regulated winding.

By reference to FIGURES 7 and 8 the invention may be now explained in its application to a grounded regulation using a V-connection. The circuit diagram (FIGURE 8) shows a two-winding transformer having non regulated primary windings with terminals U V W and reguilated secondary windings with terminals U V W each phase of the latter consisting respectively of a part 1', 1", 1'. For regulation, the adjustable secondary windings of two series transformers ZT and ZT are connected to two additional sections (in the circuit diagram to the additional sections of the phases U and W;,), the primary windings of which are fed by interlinked voltages of the non-regulated main transformer primary. The phase relations of the feeding voltages are seen from the vector diagram FIGURE 7b. The secondary windings of the series transformers ZT and ZT are adjusted by the adjustable taps St and St The latter are conductively connected and also to the third phase V Also for such a regulation it is possible to obtain a ground by using a zigzag choke.

The invention is not restricted to the star connection of the winding to be regulated but is applicable also when that winding is delta-connected. FIGURES 10 and 12 show circuit diagrams for such a case and FIGURES 9 and 11 the vector diagrams belonging thereto. According to FIGURE 10, voltages are added, to the interlinked voltages of the windings having the terminals U V W The added voltages are identical with the main transformer voltage and the teaser transformer voltage of a Scott connection, with regard to their phase position and also to their magnitude. There are connected the two adjustable secondary windings of the Scott main transformer B, the primary winding of which is fed by phase U to the terminals of the windings 1', 1", and the adjustable secondary winding of the teaser transformer H, the primary winding of which is' fed by the interlinked voltage of the phases V W to the terminal of the winding 1". For the circuit connection according to FIGURE 10 it is supposed that the secondary windings of the main transformer B as well as the secondary winding of the teaser transformer H consist of a coarse step and a fine tap. The voltage adjustment is performed by adjustable taps St St; and St According to the circuit diagram of FIGURE 12, and

I 4 t in conformity with the vector diagram of FIGURE 11, a voltage having a 180 phase shift relative to the voltage of phase U is inserted between the basic windings of the phases V W by the secondary winding of the series transformer B. At the midpoint point of its secondary voltage a voltage having the phase position of the interlinked voltage of the phases V W is added by the second-ary winding of the series transformer H. .The mid point is obtained by tapping the primary winding of an auxiliary transformer HT parallel to the effective part of the second-ary w-indingof the series transformer B. In order to get a equilateral triangle for the vectors of the interlinked voltages of the regulated system, there is inserted-between the phases W ,-U a voltage in phase with the voltage of phase U which is equal in magnitude. to the secondary voltage of the series transformer B. Such a voltage is supplied by the secondary winding of the auxiliary transformer HT. The adjustable taps designated by S1 and St According to the circuit diagram of FIGURE 14 and the vector diagram of FIGURE 13 belonging thereto, an additional voltage in phase with the voltage of the phase V is added to the voltage of hte basic winding of the phase U by the series transformer ZT and there is also added an additional voltage in phase with the voltage of the phase V to the voltage of the basic winding of the; phase W by the series transformer 2T The adjustable taps are designated by S1 and St Furthermore, it: is supposed that the primary sides of the series trans-- formers are fed by the basic winding parts of the regulated winding. Of course, the primary sides of the series transformers may also be fed by the non regulated transformer side, as it is the case in the circuit of FIGURE 8.

While the invention is shown and described by particular representative embodiments thereof, it will be obvious to those skilled in the art that many changes and modifications may be made in them without departing from this invention, using all the measures known in voltage regulation of transformers as, for instance, providing coarse and fine steps, series connection as well as an opposing connection of the parts of the winding sub-v jected to regulation or arrangement of the coarse steps in the main transformer or in the series transformers, particular reference being also made to the possibility :of transferring the taps to the primary windings of the series transformers (voltage regulation by changing the mag-f netic-flux density). In doing so the voltage divider chokes Dr and Dr in FIGURES 2 and 3 shall be replaccd,by a 33.3 percent tap on the secondary winding of the teaser. transformer and by a mid tap on the secondary winding of the Scott main transformer.

The advantages of a regulation according to this invention especially consist in a better use of the volume of the tank containing the main transformer and the series transformers, because it is possible to provide the two single-phase series transformers on the smaller side of the tank by placing them one upon another, without exceeding the loading gauge for the breadth, as is schematically shown in FIGURE 5. With a connection according to FIGURES 3, 8, l2 and 14, one phase of the expensive regulating switch can moreover be saved. A regulating switch shorter in length and therefore'a further saving of tank volume are the welcome results of such connections. A further important advantage is the fact that the conductors leading from the series transformers to the adjustable taps placed immediately near them or over them become short. In this way there are also avoided the regulating leads along the longer side of the transformer tank which require too much tank volume owing to the voltage clearances necessary between said leads and the tank wall and the neighbouring legs and which cause additional losses in the tank walls.

The main transformer illustrated in FIG. 15 has a five-legged core. Thus it is possible to dispense with a separate main transformer of theseries in the Scott eir-..

'5 cuit. This winding is placed on one outer leg of the five-legged transformer as shown. Alternatively, both outer legs may be used (not shown).

It should be noted that the magnetic flux in the outer legs is in the required phase for the Scott main transformer without any forced excitation from a tertiary winding, provided the magnetic reluctances are evenly distributed. Alternatively forced excitation may be used.

When the excitation of the outer leg or outer legs is thus positively enforced, there is also obtained the advantage that the flux in the return path is checked and, therefore, the flux distribution in the main transformer core is not controlled by the ratio of the magnetic resistance (reluctance) of yoke and outer leg but is positively enforced. In such a way the positively enforced excitation of the return path will reduce the core iron losses. The tank room saved, if a separate core for the Scott main transformer is dispensed, will, in general, be suliicient for installation of the regulating switch, especially when consisting of only two phases according to the circuit diagrams FIGURES 3, 8, 12 or 14.

This invention is also applicable if two windings of the main transformer are to be controlled. The series transformers and the tap changers may then be placed on both small sides of the main transformer. If a five-legged main transformer core is provided, each outer leg may carry the windings of at Scott main transformer. The abovementioned advantages will then also be obtained for this arrangement.

Though the inventive idea has hitherto been shown in its application to regulation of the voltage only in relation to its magnitude, it is also applicable to combined voltage and phase-angle control. As it is obvious to those skilled in this art, it is possible to obtain a regulating transformer for phase-angle and voltage control for each of the previously described circuit diagrams by a cyclic change of the basic winding parts.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A circuit for regulating transformers for three-phase circuits comprising a three-phase power transformer, having at least primary and secondary windings, two singlephase transformers and adjustable taps, said three-phase power transformer having a constant ratio of transformation, each of said two single-phase transformers having a primary and a secondary winding, said latter secondary windings being adjustable by said adjustable taps, the secondary windings of said single-phase transformers being connected in series with said secondary windings of said three-phase power transformer, said primary windings of said single-phase transformers being fed from said three-phase power transformer, the phase of the voltages feeding the primary windings of said single-phase transformers being selected and the magnitude of the secondary voltages of said. single-phase transformers adjusted by said taps to render the regulated circuit a symmetrical system.

2. A circuit for regulating transformers according to claim 1, in which said two single-phase transformers are inserted into the regulated circuit as a Scott connection, one being a teaser transformer, the other a main tran former.

3. A circuit for regulating transformers according to claim 1, in which said two single-phase transformers are inserted into the regulated circuit in the manner of a V-connection (open delta connection).

4. A circuit for regulating transformers according to claim 2, wherein said secondary three-phase power transformer windings are star-connected, said three-phase power transformer has a tertiary winding connected as a delta-connection, and secondary windings of said two single-phase transformers are inserted in Scott connection at the ground of said star-connected secondary threephase transformer windings and said primary windings of said two single-phase transformers are fed by said delta-connected tertiary windings of said three-phase transformer.

5. A circuit for regulating transformers according to claim 4, in which the main transformer of said Scott connection has two secondary windings having an equal number of turns, each adjustable by one of said adjustable taps, and said secondary of the teaser transformer is adjustable by one of said adjustable taps, and the outgoing leads of said three taps are conductively connected.

6. A circuit for regulating transformers according to claim 5', further comprising a choke, said choke being connected in parallel to the effective section of said secondary windings of the teaser transformer, and said choke having a 33.3 percent tap forming the ground of the regulated circuit.

7. A circuit for regulating transformers according to claim 4, further comprising a first choke having a center tap, said choke being connected in parallel to the effective section of said secondary windings of said main transformer of the Scott connection, and a second choke having a 33.3 percent tap, said second choke being connected in parallel to the eifective section of said secondary winding of said teaser transformer, in which further said center tap is conductively connected to said adjustable tap adjusting said secondary teaser transformer winding and said 33.3 percent tap establishes the ground of the regulated circuit.

8. A circuit for regulating transformers according to claim 4, in which a zig-zag-connected choke has its ground brought out and is fed by the three-phase side terminals of the Scott connection.

9. A circuit for regulating transformers according to claim 2, wherein the secondary three-phase transformer windings are delta-connected, said one single-phase transformer is fed by a primary voltage of said three-phase transformer and has two secondary windings having an equal number of turns, said second single-phase trans former is fed by a voltage in quadrature to the voltage feeding the first single phase transformer, said two secondary windings of said first single phase transformer are series connected to two secondary windings of the threephase transsformer, respectively, said secondary winding of said second single-phase transformer is series connected to the third secondary winding of said three-phase transformer, and the sum of the voltages of said two secondary windings relates to the voltage of said secondary winding of said second single-phase transformer as the voltage of the main transformer of the Scott connection to the voltage of the teaser transformer.

10. A circuit for regulating transformers according to claim 2, wherein the secondary three-phase transformer windings are delta-connected, said secondary winding of one single-phase transformer is connected between two secondary windings of said three-phase transformer, said primary winding of said single-phase transformer is fed by a voltage in phase with the third phase, an auxiliary transformer having a transformation ratio of 1 to l is parallel-connected to the effective section of the secondary winding of said single-phase transformer, said secondary winding of said second single-phase transformer is connected to a center tap of the primary winding of said auxiliary transformer, the secondary winding of said auxiliary transformer is connected between two other windings of said three-phase transformer, the secondary voltage of said first single-phase transformer relates to the secondary voltage of said second single-phase transformer as the voltage of the main transformer of a Scott connection to the voltage of the teaser transformer.

11. A circuit for regulating transformers according to claim 3, wherein the secondary regulated three-phase transformer windings are star-connected, said secondary windings of said two single-phase transformers are connected in series to two secondary windings of said threephase transformer, said primary windings of said singleswam phase transformers are fed by the interlinked voltages to .the third phase of said primary windings of said threephase transformer, and the outgoing leads of the adjustable taps adjusting said secondary windings are conductively connected together and to the terminal of the third phase.

12. A circuit for regulating transformers according to claim 3, wherein the secondary three-phase transformer windings are delta-connected, said secondary winding of one single-phase transformer is connected in series to one 10 secondary winding of said three-phase transformer, said primary winding of said single-phase transformer is fed by a voltage in phase with said phase, said secondary winding' of the second single-phase transformer is'-con-.

phase with the third phase.

three-phase transformer, and said primary winding of said second single-phase transformer is fedby a voltage 13. A circuit for regulating transformers according to claim 2, wherein the three-phase transformer has a fivelegged core and the windings of the main transformer of the Scott connection are placed on the outer legs of the three-phase transformer core. v

References Cited in the file of this natent I UNITED STATES PATENTS 1,847,920 Blume Mari-l, 1932 iriected inseries to a second secondarywinding of'said l5 2723352 Sealey 5 

